<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-01-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001834032</issuerCik>
        <issuerName>Constellation Acquisition Corp I</issuerName>
        <issuerTradingSymbol>CSTA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001841956</rptOwnerCik>
            <rptOwnerName>Stapp Thomas</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>181 WESTCHESTER AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 407A</rptOwnerStreet2>
            <rptOwnerCity>PORT CHESTER</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10573</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Private Placement Warrant</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2021-01-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>204198</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Ordinary Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>204198</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>204198</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to that certain Private Placement Warrants Purchase Agreement, dated January 26, 2021, by and between the Issuer and the undersigned parties thereto, the Reporting Person acquired from the Issuer 204,198 warrants of the Issuer (each, a &quot;Private Placement Warrant&quot;) for an aggregate purchase price of $306,297, as described in the Issuer's Registration Statement on Form S-1 (File No. 333-251974) filed with the Securities and Exchange Commission on January 22, 2021 (the &quot;Registration Statement&quot;).</footnote>
        <footnote id="F2">Each Private Placement Warrant is exercisable to purchase one Class A ordinary share of the Issuer (&quot;Class A Share&quot;) at an exercise price of $11.50 per share. As described in the Registration Statement, the Private Placement Warrants are identical to the warrants sold in connection with the Issuer's initial public offering (&quot;IPO&quot;), except that the Private Placement Warrants, (i) will not be redeemable by the Issuer, except as described in the Registration Statement, (ii) may not (including the Class A Shares issuable upon exercise of such warrants), subject to certain limited exceptions, be transferred, assigned or sold by until 30 days after the completion of the Issuer's initial business combination, (iii) may be exercised by the holders on a cashless basis and (iv) will be entitled to registration rights.</footnote>
        <footnote id="F3">The Private Placement Warrants will expire upon the 24-month anniversary of the closing of the Issuer's IPO if the Issuer's initial business combination has not been completed prior to such date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Thomas Stapp</signatureName>
        <signatureDate>2021-02-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
